The present invention relates to producing chlorine dioxide using expanded amorphous aluminum silicates (xe2x80x9cEAASxe2x80x9d) (CAS 93763-70-3).
Chlorine dioxide (ClO2) is a superior oxidizing agent widely used as a bleach, disinfectant, fumigant or deodorizer as it can penetrate the cell wall or membranes and cytoplasm of mold spores, bacteria and other microbiological contaminants at low concentrations.
The incorporation of chlorine dioxide or sodium chlorite in food packaging has prompted studies to determine whether residual levels of such preservatives result in a significant genetic or carcinogenic hazard to humans. Meier et al. studied the effect of subchronic and acute oral administration of chlorine, chlorine dioxide, sodium chlorite, sodium chlorate and related substances on the induction of chromosomal aberrations and sperm head abnormalities in mice. Only the highly reactive hypochlorite resulted in a weak positive effect for mutagenic potential. The other compounds, including chlorine dioxide and sodium chlorite, failed to induce any chromosomal aberrations or increased numbers of micronuclei in the bone marrow of mice. Richardson et al. reported that an extensive study of the reaction of chlorine dioxide with water borne organics by the Environmental Protection Agency confirmed this observation.
Japanese Patent Nos. 63/296,758, 63/274,434, and 57/168,977 issued to Kokai describe deodorants containing chlorine dioxide incorporated in a polymer, ceramic beads, and calcium silicate wrapped in non-woven cloth, respectively. Gels which generate chlorine dioxide for use as topical applications for disinfection are disclosed by Kenyon, et. al., Am. J. Vet. Res., 45(5), 1101 (1986). Chlorine dioxide generating gels are generally formed by mixing a gel containing suspended sodium chlorite with a gel containing lactic acid immediately prior to use to avoid premature chlorine dioxide release. Chlorine dioxide releasing gels have also been used in food preservation.
Encapsulation processes have also been used in preparing sources of chlorine dioxide. Canadian Patent No. 959,238 describes generation of chlorine dioxide by separately encapsulating sodium chlorite and lactic acid in polyvinyl alcohol and mixing the capsules with water to produce chlorine dioxide.
Tice, et al., U.S. Pat. No. 4,585,482; describe gradual hydrolysis of alternating poly(vinyl methyl ether-maleic anhydride) or poly(lactic-glycolic acid) to generate acid which can release chlorine dioxide from sodium chlorite. A polyalcohol humectant and water are encapsulated with the polyanhydride or polyacid in a nylon coating. After sodium chlorite is diffused into the capsule through the nylon wall, an impermeable polystyrene layer is coacervated around the nylon capsule. Solvents are required for reaction and application of the capsules. The capsules can be coated onto surfaces to release chlorine dioxide. Although the capsules are said to provide biocidal action for several days to months, chlorine dioxide release begins immediately after the capsules are prepared. The batchwise process used to prepare the capsules also involves numerous chemical reactions and physical processes, some of which involve environmental disposal problems. Wellinghoff, et. al., U.S. Pat. No. 5,695,814 describe methods of making a powdered biocidal composition for the release of ClO2.
There is a need for a composite that can be easily activated to initiate chlorine dioxide release in use. A composition that is composed of and generates only FDA-approved substances, or those generally recognized as safe (GRAS), is particularly needed for food packaging and other applications where the substances can be ingested by or in contact with humans.
The present invention uses expanded amorphous aluminum silicate as a vehicle for a chlorite salt. This vehicle, when exposed to moisture, releases chlorine dioxide (ClO2) for purposes of deodorization and microbial suppression, and for reducing spoilage and shrinkage for produce. Thus, where a particular area is to be deodorized or made less microbally contaminated, or where produce is to be treated, the EAAS-chlorite salt (most preferably sodium chlorite) is placed in the area to be treated and moisture is permitted to interact with the material. The moisture permits the chemical reaction (presumably acidification) of the chlorite salt to yield chlorine dioxide gas.
While normal EAAS has some inherent acidity, the inherent acidity is low enough such that, even when a chlorite salt is encapsulated in the EAAS and the resultant mixture exposed to moisture, ClO2 release is very slow and over an extended period. Under most conditions, a more rapid release of ClO2 is desired for deodorization and/or sterilization. A more rapid release of chlorine dioxide can be accomplished by first treating the native EAAS with an acid, preferably a protic acid, to acidify chemical groups of the EAAS. After native EAAS is acidified and dried, if necessary, a chlorite salt such as sodium chlorite is incorporated therein.
In another embodiment of the present invention, the chlorite salt is incorporated within the EAAS without prior acidification of the EAAS. In order to accelerate ClO2 release, the EAAS-chlorite salt mixture may be exposed to a volatile acid such as acetic acid or the like. This may be prior to or in conjunction with the exposure of the EAAS incorporated chloride salt to moisture as found in water vapor or water droplets.